1. Field of the Invention
The present invention relates to a hot dry rock generation system in which a heat carrier is made stream into the high temperature hot dry rock existing underground; the heat carrier heated by the hot dry rock is collected; and, power generation is performed by use of the heated heat carrier.                It is hereby noted that the term “invention” or “present invention” in this specification means the aspect, the mode or the embodiment disclosed by this specification.        
2. Background of the Invention
The hot dry rock generation system is conventionally known to the public (e.g. Patent References JP 1978-246403, JP1992-234576 and JP1999-223176); in the conventional hot dry rock generation system, a heat carrier is made stream into the high temperature hot dry rock deeply situated beneath the ground surface (e.g. at the depth of the 2000 to 4000 m). Hereby, the hot dry rock means high temperature rock existing underground; preferable hot dry rock is high temperature rock that includes few cracks or gaps that can contain hot-water, hot-water circulating system being not developed in the hot dry rock. In addition, in this application, the hot-water means high temperature water in which gasified steam is to be included.
Further, the recharge well and the production well are chutes (boring holes) that are bored by an excavator having a mechanism in which a rotor fitted in a long cylindrical stator revolves (e.g. Patent References JP 1998-14731). Further, steel pipes are inserted in the boring hole; concrete is poured into the space between the steel pipes and the boring hole. Thus, the water (heat carrier) tightness (regarding the wells) is achieved. Further, after the chutes are formed, the excavation is performed further deeply, by additional several meters from the bottom of the chutes; and, high pressure water is sent to the hot dry rock through the steel pipes so that high water pressure works on the bedrock of the hot dry rock, and cracks are formed in the hot dry rock.
By use of such hot dry rock as a heat source, water is converted into steam; thus, the hot dry rock generation system obtains the underground thermal energy on the ground; the hot dry rock generation system adopts a configuration such as shown in FIG. 8. As shown in FIG. 8, the hot dry rock generation system is different from the general system of the geothermal power plant in that the hot dry rock generation obtains the underground thermal energy by passing water through the hot dry rock R that existing deep underground and is provided with artificial cracks.
The recharge well 1 and the production well 2 are formed as flow passages that reach the hot dry rock R; water is charged into the recharge well 1, while hot-water is discharged through the production well 2. The recharge well 1 and the production well 2 communicate with each other via the cracks formed in the hot dry rock R.
Further, the water charged into the recharge well 1 reaches the hot dry rock R, streams through the cracks (the spaces formed with the cracks), runs upward through the production well 2, and is discharged as hot-water to the ground from the production well. The hot-water discharged on the ground is guided to the power generation plant 3 so as to drive the steam turbine and generate electric power. After being utilized in the power generation plant 3, the hot-water returns back to the collecting tank 4. The temperature of the hot-water that returns back to the collecting tank 4 exceeds 100° C. The water stored and cooled in the collecting tank 4 is sucked by the sealing water pump 5 and charged again into the recharge well 1.
In the conventional hot dry rock generation system, however, when the hot-water which temperature exceeds 100° C. is discharged toward or into the collecting tank 4, the hot-water is once set free toward the open air; due to the relieved energy, a vast amount of white smoke is generated so as to defile the landscape of the site. Further, since the water in the collecting tank 4 is placed under a boiling condition, the operators who work in the neighborhood of the collecting tank 4 are exposed to danger. Incidentally, the make-up water W is supplied to the collecting tank 4 so that the water dissipation is compensated, the water dissipation being caused by the water consumption while the water passes through hot dry rock R.